In a lighting circuit for a discharge lamp, there is often employed a protection circuit which cuts off the supply of electric power to the discharge lamp, when something wrong occurs in the discharge lamp or in the operation of the lighting circuit.
For example, the discharge lamp lighting circuit can be structured such that there is a detector for detecting the removal of the discharge lamp from a connecting member, such as a socket or the like, and, when such condition is detected, immediately stopping the supply of power to the discharge lamp.
However, in the above-structured lighting circuit, even if the discharge lamp is not removed from the connecting member, the detector may erroneously detect the removal of the discharge lamp due to vibrations, temporary poor contact or the like. As a result the power supply to the discharge lamp can be stopped or a blinking on and off of the discharge lamp can occur.